Typical gas-fired water heaters are constructed for installation and operation in indoor spaces such as basements, garages, laundryrooms, closets and the like. Many such constructions do not have a chimney available for use as a means to exhaust flue gases or products of combustion from the water heater. Accordingly, other flue exhaust systems have been developed which exhaust flue gases from the building in an alternate manner. Representative examples include the water heaters disclosed in U.S. Pat. Nos. 4,672,919 and 5,255, 665.
Since such water heaters do not utilize the natural draft afforded by a chimney, such water heaters are equipped with fans or blowers to assist the flue gases or combustion products from the upper portion of the water heater outwardly of the building. The presence of the fans or blowers presents the potential for flue gases to exhaust into the interior space if the fan or blower is not working properly or if there is blockage of the conduit extending from the fan or blower to the exterior of the building. Thus, various measures have been taken to help increase the safety factor in the operation of such water heaters.
Various detection systems have been devised to accomplish the safety goal. For example, U.S. Pat. No. 4,672,919 includes a pair of thermostats on the blower assembly, one on the top and one on the bottom, to detect blockage of the vent system. Separately, a pressure switch connected to the control valve actuates the blower when the control valve supplies gas to the main burner.
Unfortunately, control systems of this type are relatively complex from the both the mechanical and electrical perspectives. Such complexity results in a relatively large number of parts required to perform the necessary operational and safety functions. The increased number of parts results in assembly-line complexity, which increases labor costs as well as costs of materials.
Typical water heaters also utilize electro-mechanical thermostat units to detect the temperature of water in the water tank. Such thermostats have wide temperature set-point tolerances that result in wide variations in water temperatures and increased response times.